This invention relates in general to an apparatus for removing water from clay and, in particular, to an apparatus for electrokinetically removing water from a clay cake as the clay cake passes through the apparatus along a predetermined path of movement.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a dewatering apparatus through which a clay cake is directed while exposed to an electrokinetic field, to remove a portion of the water from the clay cake and thereby increase the solids content of the cake.
Clays, such as kaolin, are widely used as adsorbents, pigments, catalysts, paper fillers and the like. Such clay generally occurs in geological deposits as a mixture with inert foreign materials from which it is desirable for certain commercial applications to separate the clay material before the clay is utilized. One method of separation of the clay from the inert foreign materials is effected by dispersing the crude clay and water with the aid of dispersing chemicals such as sodium silicate, sodium hexametaphosphate, sodium tripolyphosphate and tetrasodium pyrophosphate and such clay slurry is then blunged, degritted, classified and leached to effect removal of the undesired foreign materials. Following these steps, the clay is filtered to remove the dispersing and leaching chemicals, and a somewhat solid filter cake containing 50% to 60% clay solids is produced. This 50% to 60% clay solids cake is then redispersed and sprayed dried or otherwise dried in the flocculated state.
For various economic reasons, it is desirable in the clay industry to ship clay slurries containing at least substantially 70% solids. Therefore, it is conventional in the clay art to add approximately 30% to 50% spray dried clay to a 50% to 60% solids redispersed filter cake to yield a 70% solids slurry. The addition of spray dried clay to the redispersed clay filter cake to prepare a 70% solids slurry for shipment, adds significantly to the cost of the shipped slurry due to the relatively high costs of preparing spray dried clay. The art, therefore, has been continually seeking to effect methods whereby clay filter cakes containing at least substantially 70% clay solids can be directly obtained from clay suspensions without the addition of spray dried clay.
Among the methods which have been developed to obtain a more concentrated solids clay cake has been the use of electrokinetic phenomenon such as electrophoresis and electroosmosis. Such processes are disclosed, for example, in A. C. Kunkle, U.S. Pat. Nos. 4,003,811 and 4,048,038, and A. C. Kunkle, et al., U.S. Pat. No. 4,110,189, all of which have been assigned to the Assignee of the present invention. Apparatus for separating solid particles from an aqueous suspension utilizing electrophoresis and electroosmosis are disclosed in A. C. Kunkle, U.S. Pat. Nos. 3,980,457 and 4,132,626 and A. C. Kunkle, et al., U.S. Pat. No. 4,003,819, which have similarly been assigned. Additional general descriptions of the electrophoretic and electroosmotic phenomena are found in the references referred to in the specification of A. C. Kunkle, et al., U.S. Pat. No. 4,110,189.
Heretofore in the filtration of clay suspensions, a conventional practice has been to employ a rotary drum vacuum filter. Such filters are known to those skilled in the art and disclosed, for example, in any standard text such as the Encyclopedia of Chemical Process Equipment; Ed. Wm. J. Mead; Reinhold Publishing Co., N.Y., N.Y.,; 1964, pp. 417-38; Chemical Engineer's Handbook; J. H. Perry, Ed.; McGraw-Hill Book Co., N.Y., N.Y.; 1963; pp. 19-73 to 19-86; W. L. McCabe and J. C. Smith, Unit Operations of Chemical Engineering; 2nd Ed.; McGraw-Hill Book Co., N.Y., N.Y.; 1967; pp. 880-904; A. S. Foust et al., Principles of Unit Operations; John Wiley & Sons, Inc., N.Y., N.Y., 1960; pp. 490-500.
Such rotary drum vacuum filters generally comprise a filter drum having a filter medium mounted on the external surface of the drum. The drum is rotatably mounted on a casing or housing with a vacuum being maintained within the drum interior. The drum rotates in a liquid in which solids material is suspended and, as the drum is rotated, the vacuum within the drum causes the liquid to pass through the filter medium on the external surface into the interior of the drum. A solid filter cake is thereby formed on the filter surface while the liquid filtrate is removed from the interior of the drum. Such filtration separates the liquid solids suspension into two parts: (1) a liquid filtrate which has passed through the filter medium on the exterior surface of the drum and which may contain a low concentration of solids material, dependent upon the material from which the filter medium is formed, and (2) a filter cake which is supported on the filter medium and which contains 30% or more, and generally 40-50%, of entrained suspension liquor.